Ceftaroline fosamil ((6R,7R)-7-[(2Z)-2-ethoxyimino-2-[5-(phosphonoamino)-1,2,4-thiadiazol-3-yl]acetyl]amino]-3-[4-(1-methylpyridin-1-ium-4-yl)-1,3-thiazol-2-yl]sulfanyl]-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylate; Teflaro) is a cephalosporin antibiotic which is active against methicillin-resistant Staphylococcus aureus and Gram-positive bacteria. It has the general formula
whereby the compound is generally provided in the form of its acetic acid solvate.
EP-A-1 310 502 discloses a process for preparing ceftaroline fosamil in which a side chain is first introduced into a compound having the formula (III) (Ph=phenyl, BH=benzhydryl). Because a base is generally required for this reaction step, undesired by-products can be formed. The nitrogen atom of the compound having the formula (V) is then quaternized in a subsequent reaction step using methyl iodide.

A similar reaction is also described in T. Ishikawa et al., Bioorganic & Medicinal Chemistry, 11 (2003) 2427-2437.
It was previously considered essential that the substitution reaction should be conducted before the methylation reaction because the selective methylation of the nitrogen atom in the presence of a thiol was considered difficult and the corresponding intermediates were unstable.
It was an object of the present invention to provide an improved process for producing ceftaroline fosamil which requires less reaction steps. It was a further object of the present invention to provide an improved process for producing ceftaroline fosamil which results in a lower formation of by-products.